The age limit on cancer screenings makes sense

The rationale of screening programmes for the early detection of cancer is obvious enough, and for breast cancer in particular, more than vindicated: over the past 40 years, regular screening with mammography along with improvements in treatment has resulted in a spectacular decline, by almost half, in the numbers succumbing to the illness. The merits of screening tests for cancers of the bowel, prostate and cervix may not be as dramatic, but it seems only sensible to take advantage of the opportunity when offered.

There is, however, an anomalous situation here. Cancer is an age-determined disease – the older you are, the greater the likelihood. Why, then, do screening programmes impose an upper age limit of those deemed eligible (71 for breast cancer, 75 for bowel cancer etc), thus excluding those at highest risk? 

The motive behind this seemingly ageist discrimination, one might suspect, is financial – a not very subtle way of saving the NHS money. But screening in the older age group is not necessarily advantageous, for reasons it is useful to know about. First, its potential harms are more serious. For every thousand women over the age of 70, early detection with mammography will prevent two dying from breast cancer. However, 13 would be “overdiagnosed”, thereby exposed – to no purpose – to the hazards of treatment (surgery, chemo and radiotherapy), as their cancer would never have spread or caused any problems. When diagnosed early, it’s impossible to tell these harmless cancers apart from the harmful ones.

Then there is the tricky issue of life expectancy. A healthy 75-year-old woman found to have early-stage bowel cancer and treated appropriately could anticipate living on for another 15 years (at least). Here, screening is clearly worthwhile, but not so were she to have some serious medical condition limiting her life expectancy to just five years.

In these and other ways, cancer screening for those aged 70 and above, balancing benefits against possible risks is not straightforward. So what to do? To its credit, the NHS has settled on what seems a reasonable compromise of imposing an age limit to minimise the dangers of overdiagnosis and unnecessary treatment while allowing those motivated to do so to request screening tests on an individual basis.